The following is an extract from the book Ranger Patrolling Guide
There are two types of linear danger areas (LDA’S), known and unknown. A known LDA is one that is depicted on the map and that you plan on crossing either going to or coming from the objective. With known linear danger areas you will have a predetermined near and far side rally point and a predetermined crossing point. Near and far side rally points will have a 6-digit grid, terrain feature, and a direction and distance from the crossing point. The crossing point will have a 6-digit grid and a terrain feature. When determining the near and far side rally points, you will look for the five characteristics of a good rally point. They are: Easy, Away, Away Provide, Provide. They are; easily defendable for a short period of time, Away from natural lines of drift, Away from high-speed avenues of approach, Provide good cover and concealment from both ground and air, Provides little or no tactical value to the enemy. When looking for a crossing point, you will look for a location that provides the least chance of being detected by the enemy. Good places to cross are a bend in the road, low-lying areas, and the military crest of a hill. Poor places to cross are intersections, long access of a road, and hill tops.
An unknown linear danger area is one that is not depicted on the map and that your patrol comes upon unexpectedly. For unknown linear danger areas, your crossing point is where your direction of travel crosses the linear danger area; it must be a suitable crossing point. If not, maneuver around to a better site. The near side rally point is 300m on a back azimuth from the crossing point. The far side rally point is 300m on azimuth from the crossing point.
Known and unknown linear danger areas are either going to be active or inactive. An active linear danger area is one with signs of enemy presence or use, such as footprints or tracks from a vehicle. An inactive linear danger area has no such signs. An inactive linear danger area does not warrant clearing
A linear danger area can be either man-made or natural. Man-made linear danger areas include roads, trails, and railroad tracks. Natural linear danger areas include streams, creeks, erosion ditches, and small game trails.
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